摘要:

Radio–frequency magnetron sputter epitaxy was employed for the synthesis ofn–type modulation doped Si/Si1−xGexheterostructures. Si channels were grown coherently on sputtered, compositionally graded Si1−xGexbuffers of low defect density, and remotely doped with phosphorus by plasma assisted gas phase doping. Magnetotransport measurements on these films revealed Shubnikov–de Haas oscillations in the longitudinal and the integer quantum Hall effect in the transverse magnetoresistance, demonstrating the presence of a two–dimensional electron gas. AtT=1.6 K and sheet densities of 1012 cm−2, electron mobilities as high as 15 800 cm2/V s give evidence of the excellent structural and electronic properties achievable by the sputter growth technique. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114416

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a grazing incidence x‐ray diffraction surface structure determination on a II–VI compound, namely, the CdTe(001)C(2×2) reconstructed surface, grown by molecular beam epitaxy. The structural analysis leads to a model with cadmium bridges corresponding to a coverage of 0.5 ML Cd, as expected from previous studies. This surface arrangement is accompanied by a significant relaxation of the underlying substrate down to the sixth atomic layer. Moreover, a strong anisotropy of the reconstructed domain dimensions is observed and quantified. This findings may explain the anisotropic behavior observed during homoepitaxial and heteroepitaxial growth on CdTe. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114417

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Light emitting devices were fabricated from 2,5‐dialkoxy derivatives of poly(p‐di ethynylene phenylene‐p‐di phenylene vinylene) (PDEPDPV) sandwiched between indium tin oxide (ITO) and Al. The current–voltage (I–V) curve, electroluminescence (EL) intensity‐voltage (IEL–V) curve, and the EL spectra were identical in forward and reverse bias. TheI–Vcurves were also symmetric under illumination, withI≊0 andV=0, suggesting a negligibly small internal electric field. At high bias voltage, carrier injection was found to be dominated by tunneling at the interfaces. At low bias voltage, tunneling among localized states at the Fermi level prevailed. The behavior is discussed in relation to Fermi‐level pinning at defect states in the interfaces with the ITO and Al. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114418

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A microstrip three‐pole band‐pass filter, with a midband frequency of 9.5 GHz and a fractional bandwidth of 2%, has been fabricated using double‐sided YBa2Cu3Ox(YBCO) films on MgO substrates. The nonlinear behavior of this filter was studied by intermodulation distortion measurements. The insertion loss at the midband frequency was less than 0.1 dB and the return loss was better than 15 dB throughout the passband at 55 K. This filter showed relatively high power handling capabilities, with third‐order intercept larger than +60 dBm at 55 K. The third‐order intermodulation distortion products of this filter were found to vary with frequency in the passband, being larger near each of the band edges than at the midband. These increases in the nonlinearity near the band edges are attributed to the increase in the average stored energy in the filter, which is confirmed by the increase in the group delay near the band edge. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114419

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The superconducting properties of TlBa2CaCu2O7+&dgr;(Tl‐1212) films are greatly enhanced by annealing in unreactive ambients such as nitrogen at temperatures ranging fromTa=250–600 °C. The transition temperature,Tc, of these Tl‐1212 films as‐grown in oxygen is 70 K. Annealing for 1 h at 250 °C elevatesTcabove 90 K.Tcfurther increases and sharpens forTa=600 °C. In addition, subtle changes occur in the microstructure correlating with improved critical current density. These results indicate that Tl‐1212 films may be of greater relevance for electronics applications than previously believed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114420

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Nanoscale microbridges made of NbN granular thin films were fabricated by the edge‐defined process. The diameter of NbN grains is ∼8 nm, and the size of the microbridges is ∼50 nm in width and ∼200 nm in length. We have observed a clear Coulomb blockage at 4.2 K in current–voltage characteristics. In order to investigate electrical field effects, a gate electric field was applied to the microbridge. We observed periodic conductance modulations with the gate voltage period of 15–20 V, from which the gate‐grain capacitance is estimated to be 0.01 aF. The experimental results agree with numerical simulation based on the model of a two‐dimensional array of single‐electron‐tunneling junctions. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114421

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Diamond films were synthesized by using radio frequency (RF) power in a capacitively coupled mode with a parallel plate electrode configuration in which direct current (DC) power was also applied simultaneously. This new plasma method is superior to plain DC plasma chemical vapor deposition (CVD) techniques for diamond deposition since it is very stable and seems readily scaleable. Good quality diamond films were synthesized by this modified plasma CVD method. The effect of variation of both RF and DC parameters on the deposited diamond films is discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114422

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have established ferroelectric switching and observed a novel conductance switching phenomenon in ferroelectric polymer films fabricated by the Langmuir–Blodgett technique. The films consist of 10–30 monolayers (ML) of a copolymer of vinylidene fluoride (70%) and trifluoroethylene (30%), exhibiting a first‐order ferroelectric phase transition at 70 °C and nearly rectangular ferroelectric and conductance hysteresis at 24 °C. Ferroelectric switching is accompanied by switching of the conductance by three orders of magnitude. A model describing this switching phenomenon is proposed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114423

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Homogeneous single phase Cu(InGa)Se2films with Ga/(In+Ga)=0.25–0.75 were formed by reacting Cu–Ga–In precursor films in H2Se followed by an anneal in Ar. X‐ray diffraction and Auger analysis show that the metal precursors reacted only in H2Se were multiphase films having a layered CuInSe2/CuGaSe2structure. Solar cells made with the multiphase films have properties similar to CuInSe2devices. Cells made with the annealed single phase films behave like Cu(InGa)Se2devices with the band gap expected for the precursor composition. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114424

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.114425

出版商:AIP    

年代:1995

数据来源: AIP